9 months post BBL & one cheek feels discomfort on & off. I have an enlarged lymph node in sacral area. Is it an infection?

I have no harden areas, redness, fever but I have a sensation of warmth internally but not when touching the skin. I've taken NSAIDs and applied warm compress. The "lymph node" swollen x 2 weeks now. I have an appt set up to evaluate it. Can this be a seroma, abscess, fat necrosis? How is one from the other determined if there is no area clearly visible? If antibiotics are given shouldn't the bacteria be determined?